A Galeolaria tubeworm mound being smothered by parchment worm at Kokomohua-Long Island marine reserve in the Marlborough Sounds. Photo: Supplied / LDR
An environmental group calling for control of parchment worm in the Marlborough Sounds has criticised the Marlborough District Council for years of inaction.
However, the council said it is following expert advice and is instead focused on preventing pest species from getting established.
The parchment worm is threatening the survival of some significant marine species in the sounds, particularly the Galeolaria tubeworm, a council scientist told the Environment and Planning committee in November. Three other ecologically significant species had completely disappeared from the sounds.
The Guardians of the Sounds, an environmental group, said they raised the alarm about the rapid spread of parchment worm in Tōtaranui Queen Charlotte Sound several years ago, but the council did nothing to stop the spread.
Chairman Tim Healy said the parchment worm had been devastating for sounds marine life.
"It grows into a big fat mat [and] it completely covers the seabed. The scallops can't live with it, they either die or bugger off. Most things seem to die," Healy said.
The council's principal coastal scientist, Oliver Wade, said the parchment worm was overtaking the habitats and food supply of the Galeolaria tubeworm.
"We're seeing some of these [Galeolaria] reef systems are actually in really poor condition now," Wade said.
"They're going before our eyes ... this is the last bits that we're losing of what [biodiversity] we have in the sounds."
Parchment worm was a cryptogenic species, meaning their origins were unknown so scientists could not confirm whether it was invasive or native to New Zealand.
A 2024 University of Waikato report commissioned by the council said parchment worm numbers were limited across the country until the mid-1990s, when the population suddenly exploded in the Hauraki Gulf.
A different variation of the worm was discovered in the Sounds about 1990, but also in low numbers before rapidly increasing in 2017.
The Guardians approached the council about the worm when a commerical diver noticed how scallops in the sounds had started dying, Healy said.
"We went to the council and the government about it ... and no-one seemed to know anything about it. So we kept pushing and pushing, and they couldn't get anything done at all," Healy said.
"We were astonished that there was just really no interest in it. It's in the too-hard basket, so [they] just pretend it doesn't exist."
A sampling of scallops from the sound could not definitively link the dying scallops to the spread of parchment worm.
Healy said the Guardians attempted to get some sounds residents together to remove the worms by breaking up their beds with boat anchors.
"But we were told that we would get prosecuted if we did that, because it could spread it. But by then, it was already spread anyway."
Healy said the Guardians had asked the council to conduct a study on how fast the worm was spreading and its effect on Marlborough Sounds marine life.
"We actually went out with a commercial diver and we plotted an area and we gave them ... two areas in Ruakaka Bay, one that was pristine and one that had the worm in it."
But they never heard back from the council on whether a study was conducted, Healy said.
A council spokesperson said they were first contacted by Wade about parchment worm in 2019. The Ruakaka Bay plots had been inspected by the council, but a study was not conducted due to capacity restraints.
The spokesperson said the council not discuss prosecution with the Guardians, but made them aware that if the worms spread after they tried to break the worm bed, they would be liable under section 52 of the Biosecurity Act.
Council biosecurity manager Liam Falconer said anchors were not an effective pest control tool, and had contributed to the spread of exotic caulerpa in the upper North Island.
When the presence of the Hauraki worm variant was confirmed in the Marlborough Sounds, the council was advised not to conduct pest control measures.
"The advice council received from technical experts at the time was not to undertake control of parchment worm due to the long history of it being well established in New Zealand, the lack of effective control tools on the regional scale, and the cost involved," the spokesperson said.
"Council stands by its decision not to undertake control of this widespread species, noting that it is well established throughout the Marlborough and Tasman area."
The spokesperson said the council's biosecurity team was more focused preventing new invasive species, such as Mediterranean fanworm, from establishing itself in Marlborough.
About 2500 boats were checked each year to prevent invasive species infiltrating the region. The council said they had intercepted about 80 incursions of Mediterranean fanworm since 2014.
LDR is local body journalism co-funded by RNZ and NZ On Air.
